1. Field of the Invention
The present invention relates to a trim/tilt apparatus for a marine vessel propulsion machine for an outboard motor, an inboard outdrive engine or the like.
2. Description of the Related Art
Conventionally, in a trim/tilt apparatus for a marine vessel propulsion machine, there has been one in which a cylinder apparatus is interposed between a hull and a marine vessel propulsion machine supported to the hull so as to be tiltable, and which extends and retracts the cylinder apparatus so as to actuate the marine vessel propulsion machine to trim and tilt, by controlling so as to supply or discharge a working fluid from a working fluid supply/discharge apparatus to the cylinder apparatus.
In a trim/tilt apparatus described in Japanese Patent Application Laid-Open No. 2000-233797 (Patent Document 1), the cylinder apparatus includes a housing which is used by being connected to one of a hull and a marine vessel propulsion machine and forms a large-diameter trim chamber. A cylinder is inserted into a trim chamber of the housing so as to extend and retract and forms a small-diameter tilt chamber. A large-diameter trim piston is fixed to a cylinder end portion inside the trim chamber of the housing and divides the trim chamber into a first trim chamber on a side which accommodates the cylinder and a second trim chamber on a side which does not accommodate the cylinder. A piston rod is used by being connected to the other of the hull and the marine vessel propulsion machine, and is inserted into the tilt chamber of the cylinder so as to be extensible and retractable. A small-diameter tilt piston is fixed to a piston rod end portion inside the tilt chamber of the cylinder, and divides the tilt chamber into a first tilt chamber on a side which accommodates the piston rod and a second tilt chamber on a side which does not accommodate the piston rod.
Further, in the trim/tilt apparatus described in Patent Document 1, in order to absorb an impact force of driftwood coming into collision during logging under an arbitrary trim attitude of the marine vessel propulsion machine by a flip-up of the marine vessel propulsion machine, and to bring back the marine vessel propulsion machine to an original trim attitude capable of logging after absorbing the impact force, the tilt piston is provided with a shock blow valve and a return valve. The shock blow valve is opened at a set pressure in the case where the impact force in an extending direction of the cylinder apparatus is applied when the driftwood comes into collision with the marine vessel propulsion machine, transfers the working fluid in the first tilt chamber to a side of a free piston existing within the second tilt chamber so as to allow the piston rod to be extensible, and absorbs the impact force by flipping up the marine vessel propulsion machine from the original trim attitude. At this time, the free piston stays at its position, and only the tilt piston moves. The return valve opens in the case where the tilt piston of the piston rod is going to return to its original position (the position at which the free piston stays) due to its own weight of the marine vessel propulsion machine after absorbing the impact force by the valve opening mentioned above of the shock blow valve, brings back the working fluid between the tilt piston and the free piston to the first tilt chamber, and brings back the marine vessel propulsion machine to the original trim attitude capable of logging, in which a propeller of the marine vessel propulsion machine is submerged.
However, in the trim/tilt apparatus described in Patent Document 1, in order to cope with the collision of the driftwood against the marine vessel propulsion machine, it is necessary to provide the free piston and provide the tilt piston with a return valve, so that there is a disadvantage of a heavy weight and a high cost caused by an increase in the number of parts.